1. Field of the Invention
The present invention relates to a structure of a tire to be employed for a motorcycle.
2. Description of the Related Art
As shown in FIG. 5, in a tire 1 for a motorcycle (which will be hereinafter referred to as a “tire”), a tread surface 2 takes such a shape as to be curved outward in a radial direction and a groove 3 is formed on the tread surface 2. The tire 1 is attached to the motorcycle. When the motorcycle runs, the total weight of a vehicle including the weight of a driver is applied to the tire 1. Therefore, a portion with which the tire 1 comes in contact is flattened.
When a state in which the tire 1 does not come in contact with a ground as shown in FIG. 6(a) is changed to a state in which the tire 1 comes in contact with the ground as shown in FIG. 6(b), a contact surface portion 4 is flattened and the groove 3 is also deformed elastically. More specifically, wall surfaces 5 and 6 of the groove 3 are flexed so that both of them approach each other and an opening portion 7 of the groove 3 is reduced. In other words, an opening edge portion 9 of the groove 3 is displaced by S1 outward in an axial direction of the tire 1 (the direction of an arrow 8) and an opening edge portion 10 of the groove 3 is displaced by S2 inward in the axial direction.
At this time, the tread surface 2 of the tire 1 is curved as described above. Therefore, the displacement S2 of the opening edge portion 10 is greater than the displacement S1 of the opening edge portion 9. The tire 1 rolls over a road surface. Therefore, the opening edge portions 9 and 10 periodically repeat the elastic deformation. For this reason, the opening edge portion 10 is worn more greatly than the opening edge portion 9 so that the tire 1 causes a so-called partial wear.
The tread surface 2 is curved as described above. Therefore, a length in a circumferential direction of the tread surface 2 is gradually shortened outward in the axial direction. In the case in which the tire 1 rolls over the road surface, accordingly, a slip tends to be generated between the tire 1 and the ground toward the outer portion in the axial direction over the tread surface 2. For this reason, the opening edge portion 10 tends to be worn still more greatly than the opening edge portion 9. As a result, there is a problem in that the lifetime of the tire 1 is shortened due to the partial wear.